IfcDistributionControlElement - cardinality of inverse relationship "AssignedToFlowElement"

In building automation systems, one sensor can be involved in the control of different valves. With IfcRelFlowControlElements the link between sensors and valves can be made. The description of
IfcDistributionControlElement states

Since IfcDistributionControlElement and its subtypes typically relate to many different distribution flow elements (IfcDistributionFlowElement), the objectified relationship IfcRelFlowControlElements has been provided to relate control and flow elements as required.

However, the specification says something else:

ENTITY IfcDistributionControlElement
  SUPERTYPE OF(ONEOF(IfcActuator, IfcAlarm, IfcController, IfcFlowInstrument, IfcProtectiveDeviceTrippingUnit, IfcSensor, IfcUnitaryControlElement))
  SUBTYPE OF (IfcDistributionElement);
  INVERSE AssignedToFlowElement : SET [0:1] OF IfcRelFlowControlElements FOR RelatedControlElements;

Better readable maybe in the ttl-Representation:

:IfcDistributionControlElement rdf:type owl:Class ;
                               rdfs:subClassOf :IfcDistributionElement ,
                                               [ rdf:type owl:Restriction ;
                                                 owl:onProperty :assignedToFlowElement_IfcDistributionControlElement ;
                                                 owl:allValuesFrom :IfcRelFlowControlElements
                                               ] ,
                                               [ rdf:type owl:Restriction ;
                                                 owl:onProperty :assignedToFlowElement_IfcDistributionControlElement ;
                                                 owl:maxQualifiedCardinality "1"^^xsd:nonNegativeInteger ;
                                                 owl:onClass :IfcRelFlowControlElements
                                               ] ;
                               owl:disjointWith :IfcDistributionFlowElement .

Why is a maximum cardinality specified here? Or have I got something wrong?